U.S. patent number 4,685,909 [Application Number 06/899,379] was granted by the patent office on 1987-08-11 for disposable absorbent articles.
This patent grant is currently assigned to The Procter & Gamble Company. Invention is credited to Ronald W. Berg, Robert L. Stewart.
United States Patent |
4,685,909 |
Berg , et al. |
August 11, 1987 |
**Please see images for:
( Certificate of Correction ) ** |
Disposable absorbent articles
Abstract
Absorbent articles containing both pH control agents and
substantially water-insoluble, highly neutralized hydrogel material
as a fluid-absorbing polymer are disclosed. By placing pH control
agents and hydrogel in distinct discrete zones within the article,
absorbent products such as diapers can be realized which are highly
effective for absorbing discharged body fluids and which also serve
to prevent or reduce diaper rash.
Inventors: |
Berg; Ronald W. (Fairfield,
OH), Stewart; Robert L. (Cincinnati, OH) |
Assignee: |
The Procter & Gamble
Company (Cincinnati, OH)
|
Family
ID: |
24951641 |
Appl.
No.: |
06/899,379 |
Filed: |
August 22, 1986 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
734424 |
May 15, 1985 |
|
|
|
|
Current U.S.
Class: |
604/360; 604/375;
536/34 |
Current CPC
Class: |
A61L
15/46 (20130101); A61F 5/4401 (20130101); A61F
2013/530481 (20130101); A61L 2300/21 (20130101); A61F
13/8405 (20130101); A61F 2013/8476 (20130101); A61F
2013/53051 (20130101); A61L 2300/404 (20130101); A61F
2013/51409 (20130101) |
Current International
Class: |
A61F
5/44 (20060101); A61L 15/16 (20060101); A61L
15/46 (20060101); A61F 13/15 (20060101); A61F
013/16 () |
Field of
Search: |
;604/359,360,367,368,374,375,376,377,378 ;536/34,62 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
57-45057 |
|
Mar 1982 |
|
JP |
|
58-104276 |
|
Jun 1983 |
|
JP |
|
748135 |
|
Apr 1956 |
|
GB |
|
Other References
The Newton Kansan, "Distribution Ready," Sep. 8, 1984. .
Nite Comfort.TM. Diaper Rash Buffer, undated product brochure.
.
Kaj Health Products, Inc., Press Release, "To Control & Prevent
Diaper Rash," May 13, 1985..
|
Primary Examiner: Yasko; John D.
Attorney, Agent or Firm: Allen; George W. Goldstein; Steven
J. Schaeffer; Jack D.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of the application
having Ser. No. 734,424, filed May 15, 1985 in the names of Ronald
W. Berg and Robert L. Stewart, now abandoned.
Claims
What is claimed is:
1. A disposable absorbent article useful for absorbing discharged
body fluids while also reducing or preventing diaper rash, said
absorbent article comprising
(A) a liquid impervious backing sheet;
(B) a relatively hydrophobic, liquid pervious topsheet;
(C) a flexible absorbent core positioned between said backing sheet
and said topsheet, said flexible absorbent core comprising
hydrophilic fiber material and particles of a substantially
water-insoluble, highly neutralized hydrogel material having at
least 50% of its acidic functional groups neutralized with
salt-forming cations; and
(D) one or more pH control agents suitable for maintaining skin pH
within the range of from about 3.0 to 5.5 in the presence of urine
and feces;
said substantially water-insoluble, highly neutralized hydrogel
particles and said pH control agents being non-uniformly
distributed in distinct discrete zones within said absorbent
article.
2. An article according to claim 1 wherein
(A) said substantially water-insoluble, highly neutralized hydrogel
material is selected from acrylic acid grafted starch,
polyacrylates, isobutylene maleic anhydride copolymers, and
mixtures of these hydrogel materials; and
(B) said pH control agents are selected from non-toxic,
non-irritating low molecular weight organic and inorganic acids;
non-toxic, non-irritating high molecular weight polymeric acids and
ion exchange resins and fibers in the hydrogen form.
3. An article according to claim 2 wherein
(A) the weight ratio of fiber to highly neutralized hydrogel in the
absorbent core ranges from about 50:50 to 95:5;
(B) the weight average particle size of the highly neutralized
hydrogel material in said absorbent core ranges from about 50
microns to 1 mm; and
(C) the pH control agent component comprises from about 1% to 30%
by weight of said absorbent article.
4. An article according to claim 3 wherein said pH control agent is
selected from citric acid, adipic acid, azelaic acid, malic acid,
tartaric acid, gluconic acid, glutaric acid, levulenic acid,
glycolic acid, succinic acid, fumaric acid, pimelic acid, suberic
acid, sebacic acid, and acid phosphate salts,
carboxymethylcellulose, oxidized cellulose, sulfoethylcellulose and
phosphorylated cellulose.
5. An article according to claim 3 wherein said pH control agent is
selected from polyacrylic acid and its polyacrylate derivatives and
poly(maleic acid) and its polymaleate derivatives.
6. An article according to claim 3 wherein said pH control agent is
an ion-exchanging modified cellulose material in fiber form.
7. A disposable absorbent article useful for absorbing discharged
body fluids while also preventing or reducing diaper rash, said
absorbent article comprising
(A) a liquid impervious backing sheet;
(B) a relatively hydrophobic, liquid pervious topsheet having
incorporated therein or thereon one or more pH control agents
suitable for maintaining skin pH within the range of from about 3.0
to 5.5 in the presence of urine and feces; and
(C) a flexible absorbent core positioned between said backing sheet
and said topsheet, said flexible absorbent core consisting
essentially of hydrophilic fiber material and particles of a
substantially water-insoluble, highly neutralized hydrogel material
having at least 50% of its acidic functional groups neutralized
with salt-forming cations.
8. An article according to claim 7 wherein
(A) said substantially water-insoluble, highly neutralized hydrogel
material is selected from acrylic acid grafted starch,
polyacrylates, isobutylene maleic anhydride copolymers, and
mixtures of these hydrogel materials;
(B) the weight ratio of fiber to highly neutralized hydrogel in the
absorbent core ranges from about 50:50 to 95:5;
(C) the weight average particle size of the highly neutralized
hydrogel material in said adsorbent core ranges from about 50
microns to 1 mm; and
(D) the pH control agent component comprises from about 5% to 15%
by weight of said absorbent article.
9. An article according to claim 8 wherein said pH control agent is
selected from citric acid, adipic acid, azelaic acid, malic acid,
tartaric acid, gluconic acid, glutaric acid, levulenic acid,
glycolic acid, succinic acid, fumaric acid, pimelic acid, suberic
acid, sebacic acid, and acid phosphate salts,
carboxymethylcellulose, oxidized cellulose, sulfoethylcellulose and
phosphorylated cellulose.
10. A disposable absorbent article useful for absorbing discharged
body fluids while also preventing or reducing diaper rash, said
absorbent article comprising
(A) a liquid impervious backing sheet;
(B) a relatively hydrophobic, liquid pervious topsheet; and
(C) a flexible absorbent core positioned between said backing sheet
and said topsheet, said flexible absorbent core consisting
essentially of
(i) hydrophilic fiber material;
(ii) particles of substantially water-insoluble, highly neutralized
hydrogel material distributed within at least a portion of said
hydrophilic fiber material, said highly neutralized hydrogel
material having at least 50% of its acidic functional groups
neutralized with salt-forming cations; and
(iii) one or more pH control agents suitable for maintaining skin
pH within the range of from about 3.0 to 5.5 in the presence of
urine and feces;
said substantially water-insoluble, highly neutralized hydrogel
particles and said pH control agents being non-uniformly
distributed in distinct discrete zones within said flexible
absorbent core.
11. An article according to claim 10 wherein
(A) said substantially water-insoluble, highly neutralized hydrogel
material is selected from acrylic acid grafted starch,
polyacrylates, isobutylene maleic anhydride copolymers, and
mixtures of these hydrogel materials;
(B) the weight ratio of fiber to hydrogel in the absorbent core
ranges from about 50:50 to 95:5;
(C) the weight average particle size of the highly neutralized
hydrogel material in said absorbent core ranges from about 50
microns to 1 mm; and
(D) the pH control agent component comprises from about 5% to 15%
by weight of said absorbent article.
12. An article according to claim 11 wherein said pH control agent
is selected from citric acid, adipic acid, azelaic acid, malic
acid, tartaric acid, gluconic acid, glutaric acid, levulenic acid,
glycolic acid, succinic acid, fumaric acid, pimelic acid, suberic
acid, sebacic acid, acid phosphate salts, carboxymethylcellulose,
oxidized cellulose, sulfoethylcellulose and phosphorylated
cellulose.
13. An article according to claim 11 wherein said pH control agent
is selected from polyacrylic acid and its polyacrylate derivatives
and poly(maleic acid) and its polymaleate derivatives.
14. An article according to claim 11 wherein said pH control agent
is an ion-exchanging modified cellulose material in fiber form.
15. An article according to claim 11 wherein the thickness of said
absorbent core ranges from about 5 mm to 20 mm.
16. A disposable absorbent article useful for absorbing discharged
body fluids while also preventing or reducing diaper rash, said
absorbent article comprising
(A) a liquid impervious backing sheet;
(B) a relatively hydrophobic, liquid pervious topsheet; and
(C) a flexible absorbent core positioned between said backing sheet
and said topsheet, said core at least one distinct
hydrogel-containing layer and at least one of distinct pH control
agent-containing layer; wherein
(i) said hydrogel-containing layer consists essentially of
(a) hydrophilic fiber material; and
(b) particles of substantially water-insoluble, highly neutralized
hydrogel material distributed within at least a portion of said
hydrophilic fiber material, said highly neutralized hydrogel
material having at least 50% of its acidic functional groups
neutralized with salt-forming cations; and
(ii) said pH control agent-containing layer consists essentially
of
(a) hydrophilic fiber material; and
(b) one or more pH control agents suitable for maintaining skin pH
within the range of from about 3.0 to 5.5 in the presence of urine
and feces.
17. An article according to claim 16 wherein said absorbent core
comprises a third distinct layer consisting essentially of
hydrophilic fiber material with substantially no hydrogel or pH
control agent present, said third distinct layer being positioned
between said highly neutralized hydrogel-containing layer and said
pH control agent-containing layer.
18. An article according to claim 16 wherein
(A) said substantially water-insoluble, highly neutralized hydrogel
material is selected from acrylic acid grafted starch,
polyacrylates, isobutylene maleic anhydride copolymers, and
mixtures of these hydrogel materials;
(B) the weight ratio of fiber to hydrogel in the absorbent core
ranges from about 50:50 to 95:5;
(C) the weight average particle size of the highly neutralized
hydrogel material in said absorbent core ranges from about 50
microns to 1 mm; and
(D) the pH control agent component comprises from about 5% to 15%
by weight of said absorbent article.
19. An article according to claim 18 wherein said pH control agent
is selected from citric acid, adipic acid, azelaic acid, malic
acid, tartaric acid, gluconic acid, glutaric acid, levulenic acid,
glycolic acid, succinic acid, fumaric acid, pimelic acid, suberic
acid, sebacic acid, and acid phosphate salts,
carboxymethylcellulose, oxidized cellulose, sulfoethylcellulose and
phosphorylated cellulose.
20. An article according to claim 18 wherein said pH control agent
is selected from polyacrylic acid and its polyacrylate derivatives
and poly(maleic acid) and its polymaleate derivatives.
21. An article according to claim 18 wherein said pH control agent
is an ion-exchanging modified cellulose material in fiber form.
22. A disposable absorbent article useful for absorbing discharged
body fluids while also preventing or reducing diaper rash, said
absorbent article comprising
(A) a liquid impervious backing sheet;
(B) a relatively hydrophobic, liquid pervious topsheet; and
(C) a flexible absorbent core comprising
(i) hydrophilic fiber material;
(ii) substantially water-insoluble, highly neutralized hydrogel
material having at least 50% of its acidic functional groups
neutralized with salt-forming cations; and
(iii) one or more pH control agents, suitable for maintaining skin
pH within the range of from about 3.0 to 5.5 in the presence of
urine and feces;
said highly neutralized hydrogel material and said pH control agent
being non-uniformly distributed in distinct discrete zones of said
core, said zones being defined by partitioning the flat surface of
said absorbent core into at least one area of relatively high
hydrogel concentration and at least one area of relatively high pH
control agent concentration.
23. An article according to claim 22 wherein the front two-thirds
section of said article contains substantially all of the highly
neutralized hydrogel material within said article and wherein the
rear one-third of the article contains substantially all of the pH
control agent within said article.
24. An article according to claim 22 wherein
(A) said substantially water-insoluble, highly neutralized hydrogel
material is selected from acrylic acid grafted starch,
polyacrylates, isobutylene maleic anhydride copolymers, and
mixtures of these hydrogel materials;
(B) the weight ratio of fiber to highly neutralized hydrogel in the
absorbent core ranges from about 50:50 to 95:5;
(C) the weight average particle size of the highly neutralized
hydrogel material in said absorbent core ranges from about 50
microns to 1 mm; and
(D) the pH control agent component comprises from about 5% to 15%
by weight of said absorbent article.
25. An article according to claim 24 wherein said pH control agent
is selected from citric acid, adipic acid, azelaic acid, malic
acid, tartaric acid, gluconic acid, glutaric acid, levulenic acid,
glycolic acid, succinic acid, fumaric acid, pimelic acid, suberic
acid, sebacic acid, and acid phosphate salts,
carboxymethylcellulose, oxidized cellulose, sulfoethylcellulose and
phosphorylated cellulose.
26. An article according to claim 24 wherein said pH control agent
is selected from polyacrylic acid and its polyacrylate derivatives
and poly(maleic acid) and its polymaleate derivatives.
27. An article according to claim 24 wherein said pH control agent
is an ion-exchanging modified cellulose material in fiber form.
28. A disposable absorbent article useful for absorbing discharged
body fluids while also preventing or reducing diaper rash, said
absorbent article comprising
(A) a liquid impervious backing sheet;
(B) a relatively hydrophobic, liquid pervious topsheet;
(C) a flexible absorbent core positioned between said backing sheet
and said topsheet, said flexible absorbent core consisting
essentially of
(i) hydrophilic fiber material; and
(ii) particles of substantially water-insoluble, highly neutralized
hydrogel material distributed within at least a portion of said
hydrophilic fiber material, said highly neutralized hydrogel
material having at least 50% of its acidic functional groups
neutralized with salt-forming cations; and
(D) a flexible, water-insoluble substrate positioned between said
topsheet and the skin of the wearer of the article, said substrate
containing one or more pH control agents suitable for maintaining
the wearer's skin pH within the range of from about 3.0 to 5.5 in
the presence of urine and feces.
29. An article according to claim 28 wherein
(A) said substantially water-insoluble, highly neutralized hydrogel
material is selected from acrylic acid grafted starch,
polyacrylates, isobutylene maleic anhydride copolymers, and
mixtures of these hydrogel materials;
(B) the weight ratio of fiber to hydrogel in the absorbent core
ranges from about 50:50 to 95:5;
(C) the weight average particle size of the highly neutralized
hydrogel material in said absorbent core ranges from about 50
microns to 1 mm; and
(D) the pH control agent component in the flexible substrate
comprises from about 1% to 10% by weight of said absorbent
article.
30. An article according to claim 29 wherein said pH control agent
is selected from citric acid, adipic acid, azelaic acid, malic
acid, tartaric acid, gluconic acid, glutaric acid, levulenic acid,
glycolic acid, succinic acid, fumaric acid, pimelic acid, suberic
acid, sebacic acid, acid phosphate salts, carboxymethyl cellulose,
oxidized cellulose, sulfoethylcellulose and phosphorylated
cellulose.
31. An article according to claim 29 wherein said pH control agent
is selected from polyacrylic acid and its polyacrylate derivatives
and poly(maleic acid) and its polymaleate derivatives.
32. An article according to claim 29 wherein the flexible substrate
is affixed to the topsheet of the absorbent article.
33. An article according to claim 29 wherein the flexible substrate
is not affixed to the topsheet of the absorbent article.
34. An article according to claim 29 wherein the flexible substrate
comprises a material selected from cellulose fibers, polyolefins,
polyesters and rayon.
35. A disposable diaper useful for absorbing discharged body fluids
while also preventing or reducing diaper rash, said diaper
comprising
(A) a liquid impervious polyolefin backing sheet; (B) a relatively
hydrophobic, liquid pervious topsheet;
(C) a flexible absorbent core positioned between said backing sheet
and said topsheet, said flexible absorbent core consisting
essentially of
(i) wood pulp fibers, and
(ii) particles of substantially water-insoluble, slightly
cross-linked, highly neutralized polyacrylate hydrogel material
distributed within at least a portion of said wood pulp fibers,
said polyacrylate hydrogel material having at least 50% of its
acidic functional groups neutralized with salt-forming cations,
and
(D) a flexible air-laid web of wood pulp fibers positioned as an
insert between said topsheet and the skin of the wearer of the
diaper, said substrate having distributed therein or thereon one or
more pH control agents selected from polyacrylic acid and its
polyacrylate derivatives, poly(maleic acid) and its polymaleate
derivatives, and acid phosphate salts, said pH control agents being
present in an amount suitable for maintaining the wearer's skin pH
within the range of from about 3.0 to 5.5 in the presence of urine
and feces.
36. A diaper according to claim 35 wherein said insert is
overwrapped with a liquid pervious nonwoven substrate or film
comprising envelope tissue or polyolefin.
37. A diaper according to claim 35 wherein said insert covers from
about 20% to 90% of the diaper topsheet top surface area.
38. A diaper according to claim 37 wherein said insert has a
thickness of from about 0.2 to 1.5 cm.
39. A diaper according to claim 38 wherein pH control agent is
present in said insert to the extent that pH control agent
comprises from about 5 to 15% by weight of the insert and from
about 2% to 5% by weight of the diaper.
Description
FIELD OF THE INVENTION
The present invention relates to disposable absorbent articles such
as diapers and incontinence pads. Such articles are assembled in a
manner which renders them especially effective for absorbing
discharged body fluids while at the same time preventing or
reducing diaper rash.
BACKGROUND OF THE INVENTION
Diaper rash is a common form of irritation and inflammation of
those parts of an infant's body normally covered by a diaper. This
condition is also referred to as diaper dermatitis, napkin
dermatitis, napkin rash, and nappy rash. While certainly more
common in infants, this condition is not, in fact, limited to
infants. Any individual who suffers from incontinence may develop
this condition. This ranges from newborns, to the elderly, to
critically ill or nonambulatory individuals.
It is generally accepted that true "diaper rash" or "diaper
dermatitis" is a condition which is, in its most simple stages, a
contact irritant dermatitis. The irritation of simple diaper rash
results from extended contact of the skin with urine, or feces, or
both. Diapers are worn to catch and hold the body waste, but
generally hold the waste in direct contact with the skin until
changed, i.e., in occluded fashion for long periods of time. The
same is true for an incontinence pad, or incontinence brief.
However, while it is known that the body waste "causes" diaper
rash, the precise component or components of the urine or feces
which are responsible for the resulting irritation of the skin have
not been conclusively identified. The most commonly accepted list
of factors linked to diaper rash includes ammonia, bacteria, the
products of bacterial action, urine pH, Candida albicans, and
moisture. These are generally cited in the art as being the most
likely candidates for agents or conditions which produce or
aggravate diaper rash.
It has now been discovered that a primary cause of diaper rash is a
particular set of conditions which arises as a result of prolonged
contact of skin with mixtures of feces and urine. Activity of
proteolytic and lipolytic fecal enzymes present in such a mixture
is believed to be a major factor in producing skin irritation.
Urine in contact with enzymes from feces can also result in
production of ammonia which raises skin pH. This rise in skin pH,
for example to levels of 6.0 and above, in turn increases that
fecal proteolytic and lipolytic enzymatic activity which produces
diaper rash. Urine itself can also contribute to diaper rash by
adding moisture to the diaper environment. Water, and particularly
water in the form of urine, is especially effective at diminishing
the barrier property of skin, thereby enhancing the susceptibility
of skin to fecal enzyme irritation. However, when skin pH is kept
between about 3.0 and 5.5, the skin's barrier properties can be
maintained. The foregoing diaper rash model suggests that effective
diaper rash control can be achieved by maintaining skin pH well
within the acidic range to inhibit irritation-producing enzymatic
activity while simultaneously maintaining the diaper environment as
dry as possible.
Articles, compositions and procedures which inherently tend to
lower the pH of diapered skin are known in the art. In fact, a
number of prior art references teach the addition of various acidic
pH control or "ammonia-absorbing" agents to diapers or to the
diapered skin environment. Such references include, for example,
Alonso et al., U.S. Pat. No. 4,382,919, Issued May 10, 1983;
Blaney, U.S. Pat. No. 3,964,486, Issued June 22, 1976; Bryce, U.S.
Pat. No. 3,707,148, Issued Dec. 26, 1972; and Jones, Sr., U.S. Pat.
No. 3,794,034, Issued Feb. 26, 1974.
Likewise, a number of prior art references describe absorbent
articles which are said to be especially effective in absorbing
urine and maintaining skin dryness. Frequently such articles
involve the utilization of superabsorbent polymeric material, such
as water-insoluble, slightly cross-linked hydrogel or hydrocolloid
material, that absorbs and holds many times its weight in
discharged fluid. References involving the use of such
superabsorbent polymers in diaper structures include, for example,
Harper et al., U.S. Pat. No. 3,669,103, Issued June 13, 1972;
Harmon, U.S. Pat. No. 3,670,731, Issued June 20, 1972; Masuda et
al., U.S. Pat. No. 4,076,663, Issued Feb. 28, 1978; Melican, U.S.
Pat. No. 4,232,674, Issued Nov. 11, 1980; Holtman, U.S. Pat. No.
4,333,463, Issued June 8, 1982; Mazurak et al., U.S. Pat. No.
4,381,782, Issued May 3, 1983 and Elias, U.S. Pat. No. 4,381,783,
Issued May 3, 1983.
None of the foregoing prior art references provide both especially
effective skin pH control agents and especially effective
moisture-absorbing hydrogel polymers in the same absorbent
structure. In fact, simple combination of acidic pH control agents
with superabsorbent polymer material in the same structure cannot
be accomplished without some difficulty. The preferred
moisture-absorbing hydrogel materials are not especially effective
fluid absorbers under low pH conditions. The presence of acidic
skin pH control agents, which lower pH conditions in the region of
hydrogel-moisture contact, thus tends to diminish the
moisture-absorbing effectiveness of the hydrogel materials. There
is therefore a need to identify preferred structures and
configurations for absorbent articles which contain both effective
acidic pH control agents and effective moisture-absorbing hydrogel
polymers such that each of these components can efficiently
contribute to the prevention or reduction of diaper rash. It has
not been discovered that improved diaper rash-reducing absorbent
articles containing both acidic pH control agents and
moisture-absorbing, highly neutralized hydrogel can be realized by
incorporating these materials into distinct zones or areas within
the absorbent article structure.
SUMMARY OF THE INVENTION
The present invention provides an absorbent article, such as a
diaper or incontinence pad, which is suitable for absorbing body
fluids while at the same time reducing or preventing diaper rash.
Such an absorbent article comprises a liquid impervious backing
sheet, a relatively hydrophobic, liquid pervious topsheet, a
flexible absorbent core positioned between the backing sheet and
the topsheet, and one or more pH control agents suitable for
maintaining skin pH within the range of from about 3.0 to 5.5 in
the presence of urine and feces.
The flexible absorbent core used in the structure comprises both
hydrophilic fiber material and particles of substantially
water-insoluble, highly neutralized hydrogel material. Such
hydrogel material is considered to be highly neutralized if at
least 50% of the acidic functional groups of the hydrogel material
are neutralized with salt-forming cations.
The particles of the hydrogel material and the pH control agents
are non-uniformly distributed in distinct discrete zones within the
absorbent article. Such separation of hydrogel and pH control
agents can be accomplished, for example, by incorporating the pH
control agent with the topsheet of or an insert for the article and
not in the hydrogel-containing absorbent core. Alternatively, both
pH control agent and hydrogel may be present in the absorbent core
but in separate and/or distinct layers of the core or in separate
zones of the core as defined by distinct sections of the core
surface. By separating hydrogel material and pH control agents in
this manner, skin pH control to combat diaper rash can be realized
without adversely affecting the ability of the highly neutralized
hydrogel material to absorb fluids and maintain requisite skin
dryness.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 represents a cut-away view of a diaper structure having
acidic pH control agent carried by the topsheet.
FIG. 2 represents a cut-away view of a diaper structure having a
dual-layer absorbent core comprising both an upper layer containing
acid pH control agent and a separate lower insert layer containing
hydrogel particles.
FIG. 3 represents a cut-away view of a diaper structure having its
absorbent core partitioned into distinct sections containing,
respectively, hydrogel and acid pH control agent.
FIG. 4 represents a cut-away view of a diaper structure having acid
pH control agent-containing insert positioned on top of the diaper
topsheet so that such an insert will be in contact with the
wearer's skin.
DETAILED DESCRIPTION OF THE INVENTION
The absorbent articles of the present invention can be manufactured
in the configuration of wearable disposable products which are
capable of absorbing significant quantities of water and body waste
fluids such as urine and feces. Thus such articles, for example,
may be prepared in the form of disposable diapers, adult
incontinence pads and the like.
The absorbent articles herein generally comprise three basic
structural components. One such component is a liquid impervious
backing sheet. On top of this backing sheet is placed an absorbent
core which may itself comprise one or more distinct layers. On top
of this absorbent core is placed a relatively hydrophobic, liquid
pervious topsheet. The topsheet is the element of the article which
is placed next to the skin of the wearer. In one embodiment,
described more fully hereinafter, the articles herein will include
as a fourth element a flexible substrate, e.g., an insert,
containing acid pH control agent. Such an insert can be placed on
top of the topsheet next to the skin of the wearer.
Especially preferred absorbent articles of this invention are
disposable diapers. Articles in the form of disposable diapers are
fully described in Duncan and Baker, U.S. Pat. No. Re. 26,151,
Issued Jan. 31, 1967; Duncan, U.S. Pat. No. 3,592,194, Issued July
13, 1971; Duncan and Gellert, U.S. Pat. No. 3,489,148, Issued Jan.
13, 1970; and Buell, U.S. Pat. No. 3,860,003, Issued Jan. 14, 1975;
which patents are incorporated herein by reference. A preferred
disposable diaper for the purpose of this invention comprises an
absorbent core; a topsheet superposed or co-extensive with one face
of the core, and a liquid impervious backsheet superposed or
co-extensive with the face of the core opposite the face covered by
the topsheet. The backsheet most preferably has a width greater
than that of the core thereby providing side marginal portions of
the backsheet which extend beyond the core. The diaper is
preferably constructed in an hourglass configuration.
The backsheet of the articles herein can be constructed, for
example, from a thin, plastic film of polyethylene, polypropylene,
or other flexible moisture impeding material which is substantially
water impervious. Polyethylene, having an embossed caliper of
approximately 1.5 mils, is especially preferred.
The topsheet of the article herein can be made in part or
completely of synthetic fibers such as polyester, polyolefin,
rayon, or the like, or of natural fibers such as cotton. The fibers
are typically bound together by a thermal binding procedure or by a
polymeric binder such as polyacrylate. This sheet is substantially
porous and permits a fluid to readily pass therethrough into the
underlying absorptive core. The topsheet can be made more or less
hydrophobic depending upon the choice and treatment of fiber and
binder used in the construction thereof. The topsheets used in the
articles of the present invention are relatively hydrophobic in
comparison with the absorbent core of said articles. Topsheet
construction is generally disclosed in Davidson, U.S. Pat. No.
2,905,176, Issued Sept. 22, 1959; Del Guercio, U.S. Pat. No.
3,063,452, Issued Nov. 13, 1962; and Holliday, U.S. Pat. No.
3,113,570, Issued Dec. 10, 1963, which patents are incorporated
herein by reference. Preferred topsheets are constructed from
polyester, rayon, rayon/polyester blends or polypropylene.
An absorbent core, which may itself comprise one or more separate
and/or distinct zones, e.g., layers, is positioned between the
backing sheet and the topsheet to form the absorbent articles
herein. Such an absorbent core comprises, at least in part, a
mixture of hydrophilic fiber material and particles of
substantially water-insoluble, highly neutralized hydrogel
material. This mixture will generally be in the form of a web of
the hydrophilic fibers with the discrete particles of hydrogel
dispersed therein.
The type of hydrophilic fibers is not critical for use in the
present invention. Any type of hydrophilic fiber which is suitable
for use in conventional absorbent products is also suitable for use
in the absorbent structure of the present invention. Specific
examples of such fibers include cellulose fibers, rayon, polyester
fibers. Other examples of suitable hydrophilic fibers are
hydrophilized hydrophobic fibers, such as surfactant-treated or
silica-treated thermoplastic fibers. Also, fibers which do not
provide webs of sufficient absorbent capacity to be useful in
conventional absorbent structures, but which do provide good
wicking properties, are suitable for use in the absorbent
structures of the present invention. This is so because, in the
presence of hydrogel particles, wicking properties of the fibers
are far more important than their absorbent capacity. For reasons
of availability and cost, cellulose fibers, in particular wood pulp
fibers, are preferred.
As indicated, absorbent cores formed from such hydrophilic fibers
also contain discrete particles of substantially water-insoluble,
highly neutralized hydrogel material. Such highly neutralized
hydrogel materials are those organic compounds capable of absorbing
aqueous fluids and retaining them under moderate pressures. For
good results, the hydrogels must be substantially water
insoluble.
Examples of such hydrogels include material in the form of
cross-linked polymers. Cross-linking may be by covalent, ionic,
vander Waals, or hydrogen bonding. Examples of hydrogel polymers
include ethylene maleic anhydride copolymers,
carboxymethylcellulose, polymers and copolymers of vinyl sulfonic
acid, polyacrylates, and the like. Other suitable hydrogels are
those disclosed in Assarsson et al., U.S. Pat. No. 3,901,236,
Issued Aug. 26, 1975, the disclosure of which is incorporated
herein by reference. Particularly preferred polymers for use herein
are acrylic acid grafted starch, polyacrylates, and isobutylene
maleic anhydride copolymers, or mixtures thereof.
Processes for preparing hydrogels are disclosed in Fusayoshi Masuda
et al., U.S. Pat. No. 4,076,663, Issued Feb. 28, 1978; in Tsuno
Tsubakimoto et al., U.S. Pat. No. 4,286,082, Issued Aug. 25, 1981;
and further in U.S. Pat. Nos. 3,734,876, 3,661,815, 3,670,731,
3,664,343, 3,783,871, and Belgian Pat. No. 785,858, the disclosures
of all of which patents are incorporated herein by reference.
The hydrogel materials used in the present invention are highly
neutralized hydrogels and therefore must be hydrogels which contain
neutralizable, acidic functional groups. Thus these hydrogels must
be polymers prepared from at least some monomers containing at
least one carboxylic acid, carboxylic acid anhydride or sulfonic
acid group. Generally at least 10 mole percent and more preferably
at least 50 mole percent of the hydrogel structure will be prepared
from such acid group-containing monomers.
The hydrogel material essentially used in the absorbent core of the
articles herein is highly neutralized, i.e. at least 50%, and
preferably at least 65% of the hydrogel acidic functional groups
must be neutralized with a salt-forming cation. Sutiable
salt-forming cations include alkali metal, ammonium, substituted
ammonium and amines. Neutralization can be carried out either
before or after polymerization of the acid group-containing
hydrogel material has occurred. Neutralization can be accomplished
in known manner using conventional techniques. It should be
understood that the hydrogel material employed in the present
invention must be neutralized to the extent of at least 50% prior
to contact of the hydrogel material with body fluids such as
urine.
Hydrogel material is used in the form of discrete particles in the
absorbent core of the absorbent articles herein. Such particles can
be of any desired shape, e.g., spherical or semi-spherical, cubic,
rod-like, polyhedral, etc. Shapes having a large greatest
dimension/smallest dimension ratio, like needles, flakes and
fibers, are also contemplated for use herein. Conglomerates of
hydrogel particles may also be used.
Although the absorbent cores of the present invention are expected
to perform well with hydrogel particles having a particle size
varying over a wide range, other considerations may preclude the
use of very small or very large particles. For reasons of
industrial hygiene, (weight) average particle sizes smaller than
about 30 microns are less desirable. Particles having a smallest
dimension larger than about 3 mm may also cause a feeling of
grittiness in the absorbent structure, which is undesirable from a
consumer aesthetics standpoint. Preferred for use herein are
particles having an (weight) average particle size of from about 50
microns to about 1 mm. "Particle Size" as used herein means the
weight average of the smallest dimension of the individual
particles.
The relative amount of hydrophilic fibers and hydrogel particles
used in the highly neutralized hydrogel-containing portion of the
cores of the absorbent articles herein can be most conveniently
expressed as a weight ratio of fiber to hydrogel. These ratios may
range from about 30:70 to about 98:2. Low fiber/hydrogel ratios,
i.e., from about 30:70 to about 50:50, are practicable only when
the hydrogel used possesses a low swelling capacity i.e., hydrogels
having an absorbent capacity for urine and other body fluids of
less than about 15 times their own weight (15.times.). (Absorbent
capacity data are generally available from the manufacturer of the
hydrogel or may conveniently be determined by known means.)
Hydrogels which have a very high absorption capacity (e.g.,
25.times., and which consequently exhibit a high degree of swelling
after wetting) tend to gel block when used in absorbent structure
cores at low fiber/hydrogel ratios. This phenomenon causes
undesirable, slow, diffusion type absorption kinetics. Very high
fiber/hydrogel ratios, e.g. above 95:5, on the other hand, provide
meaningful performance benefits only if the hydrogel used has a
high absorbent capacity (e.g., 25.times. for urine and other body
fluids). For most commercially available hydrogels the optimum
fiber/hydrogel ratio is in the range of from about 50:50 to about
95:5.
Based on a cost/performance analysis, fiber/hydrogel ratios of from
about 75:25 to about 90:10 are preferred. This preference is, of
course, based on the relative costs of hydrophilic fibers (e.g.
wood pulp fibers) and hydrogel. If, for example, wood pulp prices
would go up and/or hydrogel prices would come down, lower
fiber/hydrogel ratios would be more cost effective.
The density of the hydrogel-containing portion of the absorbent
structure core is of some importance in determining the absorbent
properties of the resulting absorbent structure. When hydrogel
particles are dispersed into an absorbent web of hydrophilic fibers
having a density of about 0.1 g/cm.sup.3, the admixture of the
hydrogel results in only a small increase in the amount of fluid
which is absorbed within a practicably reasonable time (e.g. 10
minutes) because the fluid uptake of such webs is slow. When the
hydrogel-containing absorbent core is densified to a density of at
least about 0.12 g/cm.sup.3, a marked increase in absorbent
capacity is observed. It is believed that densifying the web
results in better wicking of fluid into the web, so that more
hydrogel particles participate in the absorption process, which
results in a higher actual absorbent capacity. It is further
believed that a densified web may be more effective in keeping the
hydrogel particles isolated from each other. Densifying the web
further, from about 0.15 g/cm.sup.3 to about 1 g/cm.sup.3, results
in a reduction in the bulk of the structure (which is desirable
from a consumer standpoint, for aesthetics reasons), without loss
of absorbent capacity. However, above a density of about 0.6
g/cm.sup.3, further densification hardly reduces the bulk further,
because of the inverse relationship between bulk and density. The
density of the portion of the absorbent core containing highly
neutralized hydrogel particles is therefore preferably in the range
of from about 0.10 to about 0.6 g/cm.sup.3, and more preferably
within the range of from about 0.12 to about 0.25 g/cm.sup.3.
The portion of the absorbent core which contains the highly
neutralized hydrogel can be formed by airlaying a dry mixture of
hydrophilic fibers and hydrogel particles. Such a procedure is
described more fully in Procter & Gamble; European Patent
Publication No. EP-A-122042; Published Oct. 17, 1984, incorporated
herein by reference. As indicated in this reference, the webs
formed by this procedure for use in the articles herein will
preferably comprise substantially unbonded fiber and will
preferably have a moisture content of 10% or less.
As noted hereinbefore, the web formed from a mixture of hydrophilic
fibers and the highly neutralized hydrogel particles need form only
a portion of the total absorbent core used in the absorbent
articles of this invention. Other sections or zones of the
absorbent core can contain no hydrogel particles and may comprise
only hydrophilic fibers or may comprise pH control agents, with or
without hydrophilic fibers, as hereinafter more fully described.
Such distinct core sections can comprise separate and/or distinct
layers within the absorbent core or can comprise separate and/or
distinct areas or zones within the same layer.
In a preferred diaper embodiment of the present invention, the
absorbent core with all its distinct sections taken together, will
be hourglass shaped, i.e., the width of the center of the core is
substantially less than the width of the core at the ends. In a
preferred diaper embodiment, the absorbent core with all its
distinct sections and layers will have a total thickness within the
range of from about 5 mm to 20 mm, more preferably from about 7 mm
to 12 mm.
Another essential feature of the present invention is the presence
in the absorbent articles herein of one or more pH control agents.
Such agents are non-uniformly distributed within the absorbent
article and are placed in discrete zones within the article. These
zones containing pH control agent are substantially distinct from
the zones wherein the highly neutralized hydrogel particles are
placed.
The useful pH control agents are those which maintain skin pH
within the range of from about 3.0 to 5.5, and preferably from
about 3.5 to 4.5 in the presence of urine and feces. Preferably
skin pH is maintained within this range for the length of time the
diaper is worn, e.g., for at least 4 hours for daytime infant
diapers and for at least 8 hours for nighttime infant diapers.
A wide variety of non-toxic, non-irritating acidic materials which
release protons can serve as skin pH control agents. Thus these
materials can be low molecular weight organic or inorganic acids,
high molecular weight polymeric acids or ion exchange resins and
fibers in the hydrogen form.
Suitable low molecular weight organic and inorganic acid materials
include such weak acids as citric acid, adipic acid, azelaic acid,
malic acid, tartaric acid, gluconic acid, glutaric acid, levulenic
acid, glycolic acid, succinic acid, fumaric acid, pimelic acid,
suberic acid, sebacic acid and acid phosphate salts. These low
molecular weight materials may be used in combination with their
conjugate bases to provide buffer capacity. Some of these acid
materials, such as adipic acid, possess inherent buffering capacity
as a result of their relative limited water solubility.
Suitable high molecular weight polymeric acids include polyacrylic
acid and its polyacrylate derivatives, poly(maleic acid) and its
polymaleate derivatives, alginic acid, carboxymethylcellulose and
the like. Polyacrylic acid and its polyacrylate derivatives useful
as pH control agents may be cross-linked or uncross-linked and may
range in molecular weight from 1,000 to 5,000,000. Such acrylic
acid-based materials include, for example, the Carbopol resins
which are water-soluble polymers of acrylic acid cross-linked with
such materials as polyallyl sucrose and polyallyl pentaerythritol.
Poly(maleic acid) and its polymaleate derivatives useful as pH
control agents may also be cross-linked or uncross-linked and may
range in molecular weight from 1,000 to 5,000,000. Poly(maleic
acid) derivatives include poly(vinyl ether-maleic acid), and
poly(methyl vinyl ether-maleic acid) such as the resins and poly
(styrene-maleic acid) materials.
All of the foregoing higher molecular weight polymeric materials,
unlike the highly neutralized hydrogel absorbent polymers used in
the present invention, must be less than 50% neutralized and thus
predominately in the free acid form to be effective as pH control
agents in the absorbent articles herein.
One preferred type of pH control agent comprises polyacrylic acid
and polyacrylic acid derivatives. These preferred polyacrylic acid
derivatives can include the same type of starch-grafted polyacrylic
acid or polyacrylate materials as the highly neutralized hydrogel
materials used as absorbents in the present invention. Such
acidified hydrogel materials indeed do possess some degree of fluid
absorbing capacity in addition to their capacity to lower skin pH.
It should be noted, however, that when materials of this type are
used as pH control agents in the absorbent articles herein, they
must be less than 50% neutralized. Thus, in the context of the
present invention, such acidified hydrogels must always be used in
combination with the more absorbent, more fully neutralized
hydrogels hereinbefore described as the essential fluid-absorbing
hydrogel element of the articles herein.
Another preferred type of pH control agent comprises ion
exchanging, modified cellulose materials in fiber form. This
includes, for example, carboxymethylcellulose in the free acid
form, oxidized cellulose, sulfoethyl cellulose and phosphorylated
cellulose ("cellulose phosphate") prepared by conventional
techniques. Phosphorylated cellulose, for example, can be prepared
by treating cellulose with solutions of urea and phosphoric acid,
with phosphorus oxychloride and pyridine, with phosphorus
oxychloride and phosphoric acid, with phosphorus oxychloride and
dioxane or with phosphorus oxychloride alone. Examples of methods
for preparing phosphorylated cellulose ion-exchanging fibers are
described in Bernardin, U.S. Pat. No. 3,691,154, Issued Sept. 12,
1972, and Bernardin, U.S. Pat. No. 3,658,790, Issued Apr. 25, 1972.
Methods for preparing other types of ion-exchanging cellulose
derivatives are described in Sano et al., U.S. Pat. No. 4,200,735,
Issued Apr. 29, 1980, Ward et al., U.S. Pat. No. 3,854,868, Issued
Dec. 17, 1974 and Bridgeford, U.S. Pat. No. 3,533,725, Issued Oct.
13, 1970. All of the foregoing patents are incorporated herein by
reference.
Modified cellulose ion-exchanging fibers for use in their hydrogen
form as pH control agents in the present invention preferably have
an ion-exchange capacity of at least about 0.4 meq./gram, more
preferably at least about 1.0 meq./gram. Cellulose-derived pH
control agents are especially advantageous for incorporation into
the absorbent core of the articles herein since such acidic
ion-exchanging fibers can easily be admixed with the hydrophilic
fibers essentially present in the absorbent core.
The pH control agents of whatever type used in the absorbent
articles of the present invention will generally comprise from
about 1% to 30% by weight of the total absorbent article. More
preferably, such agents can comprise from about 5% to 15% by weight
of the article.
It has been discovered that the moisture-absorbing hydrogel
material and the acidic skin pH control agents hereinbefore
described can be successfully and usefully incorporated into the
same absorbent article provided such hydrogel particles and pH
control agents are non-uniformly distributed in distinct discrete
zones within the absorbent article. For purposes of the present
invention, highly neutralized hydrogel and pH control agents are
deemed to be non-uniformly distributed in the absorbent article
when there is (a) at least one zone (and generally no more than ten
zones) within the article wherein the weight ratio of hydrogel to
pH control agent is at least about 10:1, and (b) at least one zone
(and generally no more than ten zones) within the article wherein
the weight ratio of pH control agent to hydrogel is at least about
10:1.
Such non-uniform distribution of the highly neutralized hydrogel
and pH control agent can be accomplished in a number of ways. In
one embodiment, the pH control agent is distributed in or on the
topsheet of the absorbent article with little or no pH control
agent being placed in the hydrogel-containing absorbent core of the
article. An article of this type is described in FIG. 1 of the
drawings submitted herewith. This hourglass-shaped diaper structure
comprises a liquid impervious backing sheet 101 and a hydrophobic
topsheet 102. Positioned between the backing sheet and topsheet is
an hourglass-shaped absorbent core 103 containing hydrophilic fiber
material such as wood pulp fiber. Also distributed throughout the
absorbent core 103 are discrete particles 104 of substantially
water-insoluble, highly neutralized hydrogel material. Acid pH
control agent 105 suitable for maintaining skin pH between 3.0 and
5.5 is coated on or impregnated in the topsheet 102 and is thus
maintained in a distinct zone from the hydrogel particles 104 in
the diaper core.
In another embodiment, both highly neutralized hydrogel and pH
control agent may be placed in the absorbent core but in distinct
discrete zones within the core. Such separation, for example, may
be effected by placing hydrogel and pH control agent in different
layers of the core. Thus one layer of the core, preferably the top
layer, can comprise hydrophilic fiber material and pH control agent
in a weight ratio of fiber to agent of from about 10:1 to 1:1, with
substantially no highly neutralized absorbent hydrogel present.
Another layer of the core, preferably the bottom layer, can
comprise hydrophilic fiber and highly neutralized hydrogel material
in a weight ratio of fiber to highly neutralized hydrogel of from
about 10:1 to 1:1, with substantially no pH control agent
present.
A diaper article with such a layered core is depicted in FIG. 2 of
the drawings submitted herewith. This hourglass-shaped diaper
structure also comprises a liquid impervious backing sheet 201 and
a hydrophobic topsheet 202. The absorbent core of the structure
comprises two distinct layers, i.e., an upper, hourglass-shaped
layer 203 and a lower, oval insert layer 204. The upper layer 203
contains pH control agent 205 admixed therewith. The lower oval
insert layer 204 contains discrete particles 206 of substantially
water-insoluble, highly neutralized hydrogel distributed throughout
this lower oval insert layer.
In yet another embodiment, the absorbent core of the article may
comprise three distinct layers with one layer, preferably the top,
consisting essentially of hydrophilic fiber plus pH control agent,
another layer, preferably the bottom, consisting essentially of
hydrophilic fiber plus highly neutralized hydrogel and a third
layer, preferably positioned between the other two layers,
consisting essentially of hydrophilic fibers only.
In yet another embodiment, the discrete zones containing,
respectively, pH control agent and highly neutralized hydrogel
material, may comprise different portions of the absorbent article
or core thereof as defined by partitioning the flat surface of the
article or core into at least one area of relatively high hydrogel
concentration and at least one area of relatively high pH control
agent concentration. For example, the front two-thirds section of
the absorbent article, as viewed unfolded from the top, may contain
substantially all of the highly neutralized hydrogel material
whereas the back or rear one-third section of the article may
contain substantially all of the pH control agent. Size and shape
of the discrete zones of high pH control agent concentration and
high hydrogel concentration can, of course, vary according to the
intended use and size requirements of the absorbent article
desired.
A diaper article with hydrogel and pH control agent in separate
sections of the same absorbent core layer is depicted in FIG. 3 of
the drawings submitted herewith. This hourglass-shaped structure
also comprises a liquid impervious backing sheet 301 and a
hydrophobic topsheet 302. A hydrophilic fiber-containing absorbent
core 303 is positioned between the backing sheet 301 and topsheet
302. The absorbent core 303 in this embodiment comprises a
hydrogel-containing zone 304 consisting of the front two-thirds of
the absorbent core 303 and a pH control agent-containing zone 305
consisting of the back one-third of the absorbent core 303.
Discrete particles 306 of substantially water-insoluble, highly
neutralized hydrogel are distributed throughout the
hydrogel-containing zone 304. Acidic pH control agent 307 is
distributed throughout the pH control agent-containing zone
305.
In yet another embodiment, the pH control agent may be incorporated
on or in a water-insoluble, flexible substrate which is positioned
on top of the topsheet of the absorbent article next to the
wearer's skin. The highly neutralized hydrogel particles are
incorporated into the absorbent core of the article in conventional
fashion. In this manner the requisite separation of pH control
agents and hydrogel particles can be realized.
A diaper article with such an acid-containing insert positioned on
the topsheet is shown in FIG. 4. This hourglass-shaped diaper also
comprises a liquid impervious backing sheet 401 and a hydrophobic,
liquid pervious topsheet 402. Positioned between the backing sheet
and topsheet is an hourglass-shaped absorbent core 403 containing
hydrophilic fiber material such as wood pulp fiber. Distributed
throughout the absorbent core 403 are discrete particles 404 of
substantially water-insoluble, highly neutralized hydrogel
material. Positioned on top of the topsheet is a rectangular
flexible substrate 405 which has impregnated therein particles 406
of a water-soluble acid pH control agent. This substrate may be
provided as a diaper insert or liner which may or may not be
affixed to the diaper topsheet.
The water-insoluble flexible substrate used to deliver pH control
agent in this embodiment can comprise any suitable material which
will act as a carrier for the pH control agent. Thus the substrate
can be in the form of cloth, a non-woven substrate, e.g., paper, a
film, or a sponge structure. Such substrates can be constructed of,
for example, cellulose fiber, polyolefins, polyesters, rayon, and
the like.
The pH control agents utilized in the diaper insert include the
same type of materials disclosed hereinbefore for use in other
embodiments of this invention. The pH control agent can be combined
with the flexible insert substrate in any manner which provides the
pH control agent in releasable form. Thus pH control agent, in
either solid or liquid form, can be admixed with the substrate
material as the substrate is being formed. Alternatively the pH
control agent can be added to, impregnated in or sprayed on the
insert substrate after the substrate is formed.
Enough pH control agent is preferably added to the insert substrate
to provide a total concentration of pH control agent in the
absorbent articles of from about 1% to b 10% by weight of the
article, and preferably from about 2% to 5% by weight of the
article. The insert substrates themselves will generally comprise
from about 1% to 30% by weight of pH control agent, more preferably
from about 5% to 15% by weight.
The insert substrate will generally not be large enough to cover
the entire area of the article topsheet. Preferably the insert will
cover only from about 20% to 90% of the top surface area of the
topsheet on which the insert substrate is placed. Thickness of the
insert substrate can vary widely depending upon the substrate type
and the amount and type of pH control agent it carries. Insert
substrates useful herein will generally range in thickness from
about 0.2 to 1.5 cm.
A particularly preferred embodiment for the pH control
agent-containing insert substrate can be prepared by air-laying an
admixture of wood pulp fibers and particles of pH control agent to
form a flexible web structure. This structure can be used as is or
may be overwrapped with a liquid previous, nonwoven substrate or
film. Such an overwrap can comprise, for example, envelope tissue
or polyolefins such as polypropylene topsheet material.
The insert substrate can be actually secured to the topsheet of the
absorbent article in order to ensure that the insert is properly
positioned once the absorbent article is applied to the wearer.
Thus the insert may be glued to the topsheet or otherwise affixed
using two-sided adhesive tape or similar attaching means.
Alternatively the insert substrate may simply be positioned on the
absorbent article topsheet at the time the article is applied and
not affixed to the topsheet in any way.
The absorbent articles of the present invention, with their
distinct zones containing pH control agent and hydrogel material,
are further illustrated by the following examples:
EXAMPLE I
A disposable diaper product containing both a cellulose phosphate
pH control agent and particles of a starch-acrylate hydrogel
material is prepared. Such an article comprises an absorbent core
positioned between a polyethylene backing sheet and a hydrophobic,
liquid pervious non-woven rayon topsheet. The absorbent core
comprises two layers, one of which is an hourglass-shaped primary
core and the other of which is a smaller oval insert placed beneath
the primary core.
The hourglass consists of a homogeneous blend of southern soft
wood/pine fibers and fibrous phosphorylated cellulose ("cellulose
phosphate") having an ion exchange capacity of about 3.5 meq./gram.
The oval insert consists of a homogeneous blend of southern soft
wood/pine fibers and particles (250 microns) of acrylic acid
grafted starch hydrogel ("Sanwet IM-1000" from Sanyo Co. Ltd.,
Japan). The absorbent core with its two layers is overwrapped with
tissue paper.
A more detailed description of such a disposable diaper product is
set forth in Example III hereinafter. Substantially similar
disposable diapers can be prepared by replacing the cellulose
phosphate pH control agent with an equivalent amount of an acid
phosphate salt or with a low molecular weight organic acid such as
citric acid, adipic acid, azelaic acid, malic acid, tartaric acid,
gluconic acid, glutaric acid, levulenic acid, glycolic acid,
succinic acid, fumaric acid, pimelic acid, suberic acid, or sebacic
acid.
EXAMPLE II
A disposable diaper product containing both an acidified
polyacrylate pH control agent and a starch acrylate hydrogel
material is prepared. As in Example I, such an article comprises an
absorbent core positioned between a polyethylene backing sheet and
a hydrophobic, non-woven rayon topsheet. The absorbent core
comprises two layers, one of which is an hourglass-shaped primary
core and the other of which is a smaller oval insert placed beneath
the primary core.
The hourglass consists of a homogeneous blend of southern soft
wood/pine fibers and particles (300 microns avg.) of a slightly
cross-linked, completely unneutralized poly(acrylic acid) hydrogel
material. (Aqualic 4R04K1 from Nippon Shokubai K.K. Co., Ltd.,
Japan). The oval insert consists of a homogeneous blend of southern
soft wood/pine fibers and particles (250 microns) of acrylic acid
grafted starch hydrogel ("Sanwet IM-1000" from Sanyo Co. Ltd.,
Japan). The absorbent core with its two layers is overwrapped with
tissue paper.
A more detailed description of such a disposable diaper product is
set forth in Example IV hereinafter.
EXAMPLE III
Leakage and skin pH measurement studies were conducted to determine
the ability of diapers containing pH control agents and hydrogel
absorbents to lower skin pH and to absorb discharged body fluid. In
such testing, performance of the cellulose phosphate-containing
diaper of Example I was compared with that of (1) a similar product
containing no cellulose phosphate in the hourglass core and (2) a
commercially available diaper product containing a 100% wood pulp
fiber core with no pH control agent or hydrogel material. These
diaper products are more fully described in Table I
hereinafter.
TABLE I
__________________________________________________________________________
Control Diapers Hydrogel No Example I Diaper Only Hydrogel
__________________________________________________________________________
Core Composition (%) 11/76/13 CP/CF/San 84/16 CF/San 100 CF
Hourglass (%) 20/80 CP/CF 84/16 CF/San 100 CF Insert (%) 71/29
CF/San NA NA Total Product Weight (gms) 48.9 42.5 52.5 Absorb. Core
w/Tissue (gms) 34.9 33.2 43.6 Absorb. Core w/o Tissue (gms) 32.6
30.9 39.1 Hourglass (gms) 17.9 NA NA Insert (gms) 14.7 NA NA Core
Dimensions Hourglass: Length (cm) 38.1 38.1 38.1 Width (cm) 21.6
21.6 26.7 Crotch (cm) 13.3 12.7 17.1 Area (cm.sup.2) 602.6 602.6 NA
Insert Length (cm) 25.4 NA NA Width (cm) 13.3 NA NA Core Shape Oval
NA NA Area (cm.sup.2) 299.4 NA NA Basis Weight: Hourglass
(gm/cm.sup.2) 0.049 0.051 NA Insert (gm/cm.sup.2) 0.030 NA NA
Density: Hourglass (gm/cm.sup.3) 0.150 0.132 0.100 Insert
(gm/cm.sup.3) 0.180 NA NA
__________________________________________________________________________
CP = Cellulose phosphate CF = Cellulose fiber San = Sanwet 1M1000
Starch acrylate hydrogel (about 75% NA = Not Applicable or Not
Available
In the leakage and skin pH measurement testing, diapers are worn by
normal infants. The infants are allowed to play in a nursery school
setting during the test. The diapers are left on the infants until
leakage occurs. In order to speed up the test, aliquots of
synthetic urine are added at predetermined intervals.
In the particular test of this example, 25 infants were initially
impaneled and divided into three groups, with approximately 1/3
being tested with one of three test diapers on each of three
consecutive days. In this manner, at the end of the test, each
infant had been exposed to each diaper one time. On the last day of
the study, panelists' skin pHs (undiapered and diapered) were
obtained after failure of the leakage test diaper was achieved.
Results of the leakage test and subsequent skin pH measurements
taken as part of the post-leakage skin pH study are set forth in
Table II.
TABLE II ______________________________________ Example I Hydrogel
No Diaper Only Hydrogel ______________________________________
Leakage Test Results 264.1 234.3 185.2 Total Amount of Fluid Added
to Diaper at Failure (ml average) Post Leakage Skin pH Study Number
of Panelists 7 5 7 Undiapered Skin pH (avg) 4.86 4.96 4.90 Standard
Deviation 0.17 0.19 0.53 Diapered Skin pH (avg) 4.29 5.88 5.47
Standard Deviation 0.54 0.43 0.38 pH Change* (avg) -0.56 0.92 0.57
Standard Deviation 0.50 0.35 0.48
______________________________________ *pH Change = Diapered Skin
pH - Undiapered Skin pH
The Table II leakage test data indicate that the fluid-holding
capacity of the Example I diaper is not compromised by the acidic
pH buffering capacity provided by the cellulose phosphate pH
control agent in the hourglass core. This is surprising since
laboratory data would indicate that about 15% less absorbent
capacity is provided by the Sanwet hydrogel material in an acidic
environment. The post-leakage skin pH data in Table II also
demonstrate that a skin pH increase occurs with the control diapers
containing no pH control agent whereas the Example I diaper
produced a statistically significant decrease in skin pH. This
suggests that the acidic diapers are able to deliver a low pH
benefit to skin when sufficient moisture is available to allow
interaction between the diaper core and the skin.
EXAMPLE IV
Using the polyacrylate-containing diaper of Example II, leakage and
pH measurement studies were conducted in the same general manner as
described in Example III. Products tested included (1) the Example
II diaper, (2) a similar product containing no acidic polyacrylate
in the hourglass core, and (3) a commercially available diaper
product containing a 100% wood pulp fiber core with no pH control
agent or hydrogel material. These diaper products are described in
greater detail in Table III.
TABLE III ______________________________________ Control Diaper
Example Hydrogel No II Diaper Only Hydrogel
______________________________________ Core Composition Hourglass
(%) 55.4 55.4 100 Insert (%) 44.6 44.6 Hourglass Length (cm) 38.1
38.1 38.1 Width (cm) 21.6 21.6 26.7 Area (cm.sup.2) 602.6 602.6 NA
Density (g/cms) 0.150 0.150 0.100 Total Weight (gms) 18.30 18.30
43.6 Wood Pulp Fiber (gms) 14.70 15.00 NA Acidified Polyacrylate*
(gms) 4.00 -- -- Acidified Polyacrylate* (%) 21.9 0.0 0.0 Starch
Acrylate Hydrogel** -- 2.75 -- (gms) Starch Acrylate Hydrogel** (%)
0.0 15.0 0.0 Insert Length (cm) 25.4 25.4 NA Width (cm) 13.3 13.3
NA Area (cm.sup.2) 299.3 299.3 NA Density (g/cm.sup.3) 0.18 0.18 NA
Total Weight (gms) 14.7 14.7 NA Wood Pulp Fiber (gms) 10.7 12.5 NA
Starch Acrylate Hydrogel** 4.0 2.2 NA (gms) Starch Acrylate
Hydrogel** (%) 27.2 15.0 NA Total Core Core Weight (gms) 33.0 33.0
39.1 Tissue (gms) 2.3 2.3 4.5
______________________________________ Leakage and skin pH study
test results for the Table III diapers are set forth in Table IV.
*Aqualic 4R04K1 from Nippon Shokubai K.K. Co., Ltd. **Sanwet IM1000
from Sanyo Co. Ltd.
TABLE IV ______________________________________ Example No II
Diaper Hydrogel ______________________________________ Leakage Test
Results 246 204 Total Amount of Fluid Added to Diaper at Failure
(mls. avg.) Post Leakage Skin pH Study Number of Panelists 8 9
Undiapered Skin pH (avg.) 4.75 .+-. 0.24 4.77 .+-. 0.36 Diapered
Skin pH (avg.) 3.80 .+-. 0.89 5.44 .+-. 0.68 pH change* (avg.)
-0.95 .+-. 0.78 +0.68 .+-. 0.67
______________________________________ *pH change = Diapered skin
pH - Undiapered skin pH
The Table IV data also demonstrate that the acidic diaper performed
about as well as the non-acid, starch acrylate hydrogel-containing
diaper with respect to fluid absorption capacity. The skin pH
measurements again demonstrate the impact of the acid core in
lowering skin pH in the presence of discharged body fluids.
EXAMPLE V
To demonstrate the necessity of maintaining pH control agent and
fluid-absorbing hydrogel in distinct zones within the diaper, pH
measurements are made on diapers with double layer cores containing
various amounts of pH control agent and highly neutralized
hydrogel. In this study, circular 6.2 cm diameter patches of
diapers are prepared with two-layered cores, each of which layers
is 3 mm thick and each of which layers comprises 80% wood pulp
fiber and 20% of either a highly neutralized polyacrylate hydrogel
absorbent, an acidified polyacrylate hydrogel pH control agent or a
mixture of these two types of hydrogels. These patches are soaked
in four times their weight of a mixture synthetic urine, salts,
urea and urease to simulate the used diaper environment. The pH
average of five locations on the patches are measured as a function
of time. Results are set forth in Table V.
TABLE V ______________________________________ pH (avg.) Sample 0 1
2 No. Layer Composition Hour Hour Hours
______________________________________ 1 Top = 20% Aqualic* 5.4 7.7
8.0 Bottom = 20% Aqualic 2 Top = 10% Aqualic/10% Acid 5.2 6.9 7.0
Aqualic** Bottom = 10% Aqualic/10% Acid Aqualic 3 Top = 20% Acid
Aqualic 4.0 4.6 4.3 Bottom = 20% Aqualic
______________________________________ *Aqualic is a slightly
crosslinked polyacrylate neutralized to the extent of about 75% and
is marketed under the tradename Aqualic 4R04K1 by Nippon Shokubai
K.K. Co. Ltd., Japan. **Acid Aqualic is a slightly crosslinked,
poly(acrylic acid) prepared by acidifying the polyacrylate material
marketed under the tradename Aqualic 4R04K1 by Nippon Shokubai K.K.
Co. Ltd., Japan.
The Table V data clearly show the effect of separating pH control
agent and absorbent hydrogel in the diaper core. In Sample 1, the
two layers of the diaper core are identical and contain no pH
control agent. Diaper pH rises in the presence of the synthetic
urine, urea and urease. In Sample 2, the two layers of the diaper
core are also identical, each containing a homogeneous mixture of
highly neutralized absorbing hydrogel and acidified hydrogel pH
control agent. Although diaper pH is maintained at a lower level by
this acid-containing diaper core, a significant pH rise is still
observed. In Sample 3, the acidic hydrogel pH control agent and the
highly neutralized fluid-absorbing hydrogel are kept in separate
layers of the diaper core. This configuration serves to maintain
diaper pH at significantly lower levels than do the configurations
of Samples 1 and 2.
EXAMPLE VI
A flexible substrate suitable for use as a pH control
agent-containing diaper insert is prepared by air-laying a web of
cellulose fiber (airfelt), which web has dimensions of 10 inches
(25.4 cm).times.4.5 inches (11.4 cm).times.0.20 inches (0.50 cm)
and a density of about 0.1 g/cm.sup.3. Polyacrylic acid (Acrysol
LMW-45, 15% neutralized) is uniformly distributed throughout the
substrate as a pH control agent by airlaying a dry mixture of the
airfelt and particles (125 to 700 microns) of the pH control agent.
The insert substrate thus contains about 94% by weight airfelt and
6% by weight of the polyacrylate pH control agent. The finished
insert is prepared by wrapping this substrate in polypropylene
diaper topsheet material (8 mils) and melt-bonding the overwrap at
the ends.
An absorbent article of the present invention is prepared by
positioning this insert substrate on top of the topsheet of a
conventional hydrogel-containing diaper (e.g. ULTRA PAMPERS.RTM.)
which utilizes an absorbent core comprising particles of
polyacrylate hydrogel material admixed with airfelt. In this
manner, the polyacrylate pH control agent comprises about 1.2% by
weight of the insert/diaper combination. Such an insert/diaper
combination provides effective skin pH control without significant
loss of absorbent capacity of the diaper.
Substantially similar absorbent articles are realized when, in the
above-described insert substrate, the polyacrylate pH control agent
is replaced with an equivalent amount of poly(vinyl-ether-maleic
acid) [Gantrez AN-119], ethylene-maleic acid copolymer [EMA-1103]
or combination of sodium dihydrogen phosphate and disodium hydrogen
phosphate.
EXAMPLE VII
Using the leakage and skin pH tests as generally described in
Example III, the effect of using a diaper liner similar to that of
Example VI with a hydrogel-containing diaper is determined. A
control diaper similar to the hydrogel-only diaper of Table I
(containing a polyacrylate hydrogel instead of a starch acrylate
hydrogel) is tested for both leakage and pH control in comparison
with that same diaper having a pH control insert positioned on the
diaper topsheet. Such an insert, similar in composition to that
described in Example VI, contains 6% polyacrylate (15% neutralized)
in an airfelt substrate. This insert is positioned on top of the
topsheet of the control diaper and is then placed next to the
wearer's skin when the diaper is applied.
Results of the leakage and skin pH testing is shown in Table
VI.
TABLE VI ______________________________________ Control Control
plus Diaper Insert ______________________________________ Leakage
Test Results 189 225 Total Amount of Fluid Added to Diaper at
Failure (mls. avg.) Post Leakage Skin pH Study Number of Panelists
9 9 Undiapered Skin pH (avg.) 4.81 .+-. 0.31 4.79 .+-. 0.61
Diapered Skin pH (avg.) 5.62 .+-. 0.43 4.76 .+-. 0.75 pH change*
(avg.) +0.81 .+-. 0.43 -0.03 .+-. 0.83
______________________________________ *pH change = Diapered skin
pH - Undiapered skin pH
The Table VI data demonstrate that the diaper with insert performed
as well as, and in fact somewhat better than, the polyacrylate
hydrogel-containing control diaper with respect to fluid absorption
capacity. The skin pH measurements demonstrate the impact of the
insert in lowering skin pH in the presence of discharged body
fluids.
* * * * *